[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: weird jurassic dinobird with very weird feathers

Tim Williams wrote:

<Speaking generically for short-tailed non-avian theropods... a shorter tail 
may not necessarily result in an anteriorized center of gravity, if the gut was 
expanded to accommodate an herbivorous diet. This appears to have been what 
happened in therizinosauroids, for example. So the tail could get shorter, 
because the expanded viscera contributed more posterior 'ballast'.>

  We actually only have one therizinosaur with a decent tail, and it seems to 
be a basal taxon. We assume reduction was occuring with a reasonable certainty, 
but after *Beipiaosaurus*, graviportality seems to have coincided with 
elevation of the dorsum and MASSIVE pneumatization of the vertebrae, which 
helps posteriorize the center of gravity back in front of the hips (but this is 
in the bulkier, bigger taxa). This is quite different from the condition in 
this taxon, if it had such a distinctly short tail. shortening and elevation of 
the dorsum coincide also with shortening of the dorsals and incorporation of 
the dorsals into the elevated cervicals, as in *Nanshiungosaurus*. I suspect 
the condition in the tail here is nothing of the sort. I would also like to 
note that the apparent transverse processes of the caudals in the short section 
are not inconsistent with their identification as distal caudals in a 20+ 
sequence, as such occurs in oviraptorosaurs,
 which have also undergone a distal shortening of the tail, production of a 
pygostyle, and so forth. The condition does seem to be distinct from what we 
see in *Scansoriopteryx*'s tail, but as I lack my old files, I cannot check the 
original photos.


Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)